Glitch

A glitch, also known as bug, is a software error that can lead to unintended behavior in software like the Pokémon games. It can be triggered from mistakes within the game's code or by exploits that were not anticipated by the programmers, thus causing the game to react unexpectedly. Glitches present in Pokémon games can have a variety of effects, such as the disruption of graphics or audio effects, the appearance of glitch Pokémon, or the corruption of save data.

When noticed, glitches may be fixed by its developers in later releases of a game or derivative games. In some games, such as Pokémon Ruby and Sapphire and Pokémon X and Y, patches are released that fix glitches in Pokémon games directly.

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Glitch Pokémon

Glitch Pokémon are caused by glitches that have the game erroneously read placeholder data or non-Pokémon data as Pokémon data. Although many glitch Pokémon draw all their characteristics from data intended to be used elsewhere, some glitch Pokémon may have partially defined characteristics that are not intended to be accessed in-game: for example, in the case of MissingNo., its name is well-defined, but its base stats are read from data intended to represent the parties of several Bikers.

Glitch moves

A glitch move is a move not intended to be part of the game, but accessible via glitches or cheating devices. While some glitch moves have no effect whatsoever, others may cause the game to freeze when attempting to perform them.

Usually, only glitch Pokémon will learn glitch moves. However, Ditto can be taught the glitch move -- by a glitch in Generation I. Additionally, another glitch present in the Time Capsule allows Pokémon that evolve by trading to be taught several glitch moves.

Glitch types

Glitch types are types that are solely used for glitch Pokémon or glitch moves. The Bird type is a leftover type thought to be a beta version of the Flying-type. All other glitch types are caused by erroneously reading other data as a type. Unlike regular types, glitch types often do not have any weaknesses, resistances, or immunities.

Glitch items

Placeholder items are often intentionally left in the game's code to prevent the game from crashing if the data is accessed, but without the intention to be accessible in-game. Placeholder items, such as the Teru-sama item in Generation II, often appear at the end of the games' internal item lists.

Glitch characters

In Generation I and Generation II, invalid values being interpreted as text (common in the names of glitch Pokémon and items) can cause portions of graphical assets, such as overworld tiles or HP bars, to be displayed as text.